When one intelligent life form greets another intelligent life form the first two words that are used are “Hello” and “Breed”.

Hello is used because it is a greeting that is a non-offensive acknowledgement of the other life form. Breed is used because it is an encouragement of the other life forms continuation and advancement.

In the Australian vernacular the word “G’day” is used in place of the word Hello. The “G” in “G’day”, does away with the superior, righteous, judgemental and virtuous associations with the word “Good”. The use of the abbreviated “G” in “G’day” gives the listener permission and logical reason to interpret the “G” as referring to the more informal meanings of the word “Good”, such as happy, great, OK, courteous, and kind-hearted.

“Day” is intelligent because it recognises a common element of the Universe which is that life forms are surrounded by planets that have periods of night and day. “Day” does not exclusively describe a specified length of time; rather it is a word that describes that which is frequent, persistent, constant, regular, habitual and universally overt to intelligent life forms everywhere in our Universe.

Australians use “Mate” in place of the word Breed. Mate is a very intelligent and clever word because Mate encompasses all that is in the word Breed, and at the same time easily communicates the comforting affirmation that you are my friend.

G’day Mate is the most intelligent greeting that has ever been uttered by humanity.

What many of us (Americans) believe to be a popular greeting in Australia. Many people get this idea from the media, which makes it seems like every time you see an Australian person they will say this.
NOT TRUE!
I spent 2 weeks there and didn't here that ONCE!
Yes, they say mate and an occasional g'day but I never heard them together.
It's more of a stereotype than anything else.

American (sees Australian, wants to make it look like
Americans know anything about other cultures): G'day Mate!